Neuronal activation has been associated with a number of normal biological processes, such as the use of memory in learning behaviors and responsiveness to sensory stimuli (Sharp et. al. (1989) J. Comp. Neurol. 284: 621-36). Identification of changes in neuronal activation has allowed the association of behavioral and physiological activity with certain regions of the mammalian brain. This technique has been used to identify brain regions active in normal biological processes such as male sexual behavior (Bialy and Kaczmarek (1996) Acta. Neurobiol. Exp. 56: 567-77), activation of neuroendocrine systems (Hoffman et. al. (1993) Front. Neuroendocrinol. 14: 173-213), and the physiological response to injury (Dubner and Ruda (1992) Trends Neurosci 15: 96-103).
Neuronal activation has also been implicated in abnormal biological processes. The ability to measure neuronal activity in mammalian brain tissue has allowed the association of regions of the brain with particular disorders. For example, characteristic patterns of neuronal activation in specific frontal lobe and basal ganglia circuits are observed in obsessive compulsive disorder (Otto (1992) Psychiatr. Clin. North Am. 15: 825-48). Studies examining mammalian models for Parkinson's disease have found that neuronal activities of the caudate nucleus decreased, activity of the pars reticula of the substantia nigra and the internal segment of the globus pallidus increased, and neurons of the ventromedial nucleus of the thalamus depressed markedly (Yoshida M (1993) Adv Neurol 60: 71-77). Imaging studies and pathological reports suggest that neuronal activity may be altered in certain temporal limbic regions (Reynolds G. P. (1989) Br. J. Psychiatry 155: 305-16).
A great deal of evidence has linked neuronal activation events to the regulation of gene expression. The expression of certain genes has been found to vary dramatically upon neuronal activation. Detecting levels of expression of these genes may therefore be useful as an indirect determination of neuronal activity in brain tissue.